Modern mobile communication devices often comprise an antenna, e.g. a Planar Inverted F Antennas (PIFA), that is susceptible to detuning due to changes in the antenna's environment. To improve the radiation characteristics of such an antenna the mobile communication device can comprise an adaptive impedance control system. The impedance control system can comprise an impedance measurement system to measure the actual impedance of the signal path terminated with the antenna.
U.S. Pat. No. 6,822,433 B1 shows a gain and phase detector circuit that can be utilized as an impedance measurement system. The detector circuit has an output for providing a ratiometric gain measurement and an output for providing phase information. Each output is connected to two amplifier chains.